The nonvolatile memory can retain the stored information even when power off and also can be rewrote the information several times when power is on. Due to the physical limitation of the nonvolatile memory, the thickness of the tunneling oxide layer will be decreased when the dimension of the device is decreased. The tunneling oxide layer also undergoes several times of fast read/write process. Once the leakage path of the tunneling oxide layer is created, the charges stored in the floating gate will be released away and the information will be erased. In one aspect, the data retention of the memory will be degraded, when the device has the thinner oxide layer. In another aspect, the writing speed of the charge gets slow when the thickness of the oxide layer is increased to improve the storage ability. Therefore, there is a compromise between the speed, reliability, and the data retention of the memory device.
There are two ways of the conventional method for programming the nonvolatile memory: one is Fowler-Nordheim tunneling program process, and the other is the channel-hot-electron (CHE) program process. The CHE program process writes in data faster but consumes more energy when several cells are programmed at the same time. The energy consumption of the FN (Fowler-Nordheim) tunneling program process is less and several cells can be programmed at the same time, but the voltage of program is larger and the speed of program is slower. To increase the speed and decrease the voltage of the FN tunneling program process, the thickness of the tunneling oxide layer needs to be decreased and the data retention of the memory will be decreased.
Therefore, there is a need to provide a method for programming a nonvolatile memory to resolve the above-mentioned problem.